Gas measurement system

ABSTRACT

A gas measurement system of this invention includes a detector assembly having a beamsplitter adapted to separate infrared radiation into a first beam and a second beam and a mirror adapted to receive the first beam from the beamsplitter. The first and second beams are directed to first and second detectors that are disposed in a common plane. In one embodiment, the optical elements are provided on or in an optical block. In another embodiment, the gas measurement system includes a housing that contains an infrared absorption gas measurement assembly, a luminescence quenching gas measurement assembly, and a processor that is programmed to measure gas constituents of a gas flow based on an output of the infrared absorption gas measurement assembly and the luminescence quenching gas measurement assembly.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation-In-Part under 35 U.S.C. § 120 fromU.S. patent application Ser. No. 10/792,180, filed Mar. 3, 2004, whichclaims priority under 35 U.S.C. § 119(e) from provisional U.S. patentapplication No. 60/452,656 filed Mar. 7, 2003, and is also aContinuation-In-Part under 35 U.S.C. § 120 from U.S. patent applicationSer. No. 10/781,382, filed Feb. 18, 2004, which claims priority under 35U.S.C. § 119(e) from provisional U.S. patent application No. 60/449,428filed Feb. 21, 2003, the contents of each of these applications areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a mainstream respiratory gasmeasurement system with integrated signal processing and improvedoptical design, and to a method of assembling such a system.

2. Description of the Related Art

Respiratory gas measurement systems comprise gas sensing, measurement,processing, communication, and display functions. They are considered tobe either diverting, i.e., sidestream, or non-diverting, i.e.,mainstream. A diverting gas measurement system transports a portion ofthe sampled gases from the sampling site, which is typically a breathingcircuit or the patient's airway, through a sampling tube, to the gassensor where the constituents of the gas are measured. A non-divertingor mainstream gas measurement system does not transport gas away fromthe breathing circuit or airway, but measures the gas constituentspassing through the breathing circuit using a gas sensor disposed on thebreathing circuit.

Conventional mainstream gas measurement systems include a gas sensing,measurement and signal processing components required to convert thedetected or measured signal, for example a voltage, into a value, suchas transmittance, that may be used by the system to determine aconstituent of a gas being measured. In a conventional mainstream gasmeasurement system, a gas sensor is coupled to a sample cell that isplaced at the breathing circuit. The gas sensor located on the airwayadapter disposed in the breathing circuit only includes the componentsrequired to output a signal corresponding to a property of the gas to bemeasured. Placement of the sample cell directly at the breathing circuitresults in a “crisp” waveform that reflects in real-time the partialpressure of the measured gas, such as carbon dioxide, within the airway.The sample cell, which is also referred to as a cuvette or airwayadapter, is located in the respiratory gas stream, obviating the needfor gas sampling and scavenging, as required in a sidestream gasmeasurement system.

For a conventional gas measurement system that is capable of measuringcarbon dioxide, the gas sensor includes a source that emits infraredradiation, which includes the absorption band for carbon dioxide. Theinfrared radiation is emitted in a direction that is normal to the flowpath of the respiratory gas stream. Carbon dioxide within the sample gasabsorbs the radiation at some wavelengths and passes other wavelengths.The conventional gas sensor includes photodetectors that measure thetransmitted radiation. A multi-conductor, flexible cable transmits theamplified detected signals from the gas sensor to a host system ormonitor, from which the partial pressure of carbon dioxide is calculatedand displayed graphically in the form of a capnogram.

A conventional mainstream host system contains the electronics thatcontrol the emitter in the gas sensor, and provides the gas measurementfunctions based on the output signals from the detector. Mainstream gasmeasurement systems known in the art transmit analog signals along acable, typically 6 to 8 feet in length, between the host system and thegas sensor and, as such, are susceptible to electromagnetic interference(EMI). This is particularly important given the trend towards requiringcompliance with increased electromagnetic immunity levels ininternational medical device standards. An example of such conventionalmainstream gas measurement systems are shown in U.S. Pat. No. 4,914,720issued to Knodle et al and U.S. Pat. No. 5,793,044 issued to Mace et al.

With the measurement and signal electronics located in the host system,existing mainstream gas measurement systems are complex and costly tointerface to host systems. The host system conventionally includescircuitry to perform functions such as (1) creating timing signals; (2)supplying pulsatile power to a solid state infra-red emitter; (3)measuring and precisely controlling the temperature of the infra reddetectors; (4) measuring and controlling an airway adapter heater; (5)signal conditioning including filtering and programmable gain setting;and (6) watchdog circuitry to prevent accidental destruction of theinfra-red emitter.

Additionally, to be accepted in clinical use, a mainstream gasmeasurement system must be designed in a robust manner such that it isunaffected by typical mechanical abuse and environmental variations intemperature and humidity. The instrument, or at least the gasmeasurement system portion of the instrument, must be small and lightweight so as to not interfere with the motions of the patient, or withother medical equipment or treatments.

Given these known complexities of conventional gas measurement systems,it is desirable to provide a mainstream gas measurement system that issimpler to interface to host systems. It is also desirable that such asystem provide improved methods of assembly over known gas measurementsystems.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a gasmeasurement system that overcomes the shortcomings of conventional gasmeasuring systems. This object is achieved according to one embodimentof the present invention by providing a gas measurement system thatincludes a beamsplitter adapted to separate infrared radiation into afirst beam and a second beam, a mirror adapted to receive the first beamfrom the beamsplitter, a first filter adapted to receive the first beamfrom the mirror, a second filter adapted to receive the second beam fromthe beamsplitter, a first detector adapted to receive the first beamfrom the first filter, and a second detector adapted to receive thesecond beam from the second filter. The first detector and the seconddetector are disposed in a common plane. This configuration for thedetectors causes both detectors to “see” the same image, whichcontributes to the accuracy of the gas measurement system.

In a further embodiment, the gas measurement system includes an opticalblock. A beam splitter is disposed within the optical block, and amirror is disposed on the optical block. At least two filters areoperatively coupled to the optical block. This configuration of thedetector assembly in the gas measurement system provides a discreteassembly for the detector assembly, so that it is easily replaced orserviced, easy to manufacture, and improves optical performance byattaching the optical elements of the detector assembly to a commonframe so that the elements are accurately aligned with one another.

A still further embodiment of the present invention is directed to a gasmeasurement system assembly that includes a generally U-shaped housingadapted to be mounted on an airway adapter. The housing contains aninfrared absorption gas measurement assembly and a luminescencequenching gas measurement assembly. The housing also contains aprocessor that is programmed to measure gas constituents of a gas flowin the airway adapter based on an output of the infrared absorption gasmeasurement assembly and the luminescence quenching gas measurementassembly.

These and other objects, features and characteristics of the presentinvention, as well as the methods of operation and functions of therelated elements of structure and the combination of parts and economiesof manufacture, will become more apparent upon consideration of thefollowing description and the appended claims with reference to theaccompanying drawings, all of which form a part of this specification,wherein like reference numerals designate corresponding parts in thevarious figures. It is to be expressly understood, however, that thedrawings are for the purpose of illustration and description only andare not intended as a definition of the limits of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a gas measurement system coupled to ahost system and configured to be removably secured to an airway adapterassembled with the components of a patient breathing circuit accordingto the principles of the present invention;

FIG. 2 is a perspective view of the gas measurement system configured tobe coupled to a host system;

FIG. 3 is a perspective view of the gas measurement system configured tobe removably secured to an airway adapter;

FIG. 4 is an exploded view of a gas measurement system with a cover andgas measurement system electro-optical assembly shown;

FIG. 5 is an exploded view of a gas measurement system electro-opticalassembly;

FIG. 6 is an exploded view of a gas measurement system with the cover,electronic circuit boards, and gas measurement system optical assemblyshown;

FIG. 7 is an exploded view of the gas measurement system opticalassembly with the structural base member, detector assembly, and sourceassembly shown;

FIG. 8 is an exploded view of the detector assembly;

FIGS. 9 and 10 are exploded views of the optical housing assemblyportion of the detector assembly;

FIG. 11 is a cross-sectional view of the assembled optical housingassembly;

FIG. 12 is an exploded view of the source assembly;

FIG. 13 is an exploded view of the emitter housing portion of the sourceassembly;

FIG. 14 is a cross-sectional perspective view of the assembled gasmeasurement system along line 14-14 of FIG. 4;

FIG. 15 is a flattened view of the assembled components of the gasmeasurement system prior to placement in the housing;

FIG. 16 is a ray tracing of the optical path within the gas measurementsystem according to the principles of the present invention;

FIG. 17 is a block diagram of the gas measurement system according tothe principles of the present invention;

FIG. 18 is a schematic diagram of a four channel optical system in aplain linear configuration for the optical assembly of the detectorassembly according to the principles of the present invention;

FIG. 19 is a chart showing one embodiment of the beam splitterwavelengths relative to the filter wavelengths;

FIG. 20 is a schematic diagram of a four channel optical system in azigzag configuration;

FIG. 21 is a schematic diagram of a four channel optical system in asquare array configuration;

FIG. 22 is a schematic diagram of a four channel optical system in alinear system with lenses configuration;

FIG. 23 is a schematic diagram of a four channel optical system in azigzag with lenses configuration;

FIG. 24 is a schematic diagram of a four channel optical system in adogleg configuration;

FIG. 25 is a schematic diagram of a four channel optical system in asnake configuration;

FIG. 26 is a schematic diagram of a four channel optical system in atunnel configuration; and

FIG. 27 is a side view of an embodiment of a four channel optical systemin a linear configuration.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

A gas measurement system 100 according to the principles of the presentinvention includes all of the signal and data processing required toproduce continuous values of a partial pressure or concentration of agas flowing through an airway adapter in fluid communication with apatient's airway. The gas measurement system is located on a“measurement head” that fits onto an airway adapter. The gas measurementsystem includes the electronic circuitry required to measure and computea continuous value for infrared absorbing gases, such as carbon dioxide,and luminescence quenching gases, such as oxygen, and interface the gasmeasurement system to a host system. In an exemplary embodiment, gasmeasurement system 100 acquires and processes the analog signals, thentransmits digitized patient parameters and waveforms through aninterface cable 120 as a serialized data stream.

The gas measurement system of the present invention eliminates the needfor an additional electronics board inside a host system that wouldotherwise be required to process the signal output from the detector,thus conserving space within the host system and reducing costs to theend user. Through efficiencies in the design and throughminiaturization, the resulting gas measurement system is nearly as smalland lightweight as existing mainstream gas measurement sensors. Theaddition of the signal processing without any increase in size or weightare particularly important in applications in which the gas measurementsystem is employed with an airway adapter in close proximity to apatient's face at the distal end of an endotracheal tube or a nasalcannula to monitor a patient's breathing.

An exemplary airway adapter 40 and a gas measurement system 100constructed in accord with, and embodying, the principles of the presentinvention are shown in FIGS. 1-3. Conventional gas measuring systems donot locate the signal processing and control electronics in the gasmeasurement system, but locate any such feature in the host system. Thepresent invention takes advantage of highly integrated digital signalprocessing (DSP) technology to perform many of the complex electronicinterface functions within a small single chip processor that includesprogram and data storage as well as analog to digital conversion.

Many of the efficiencies obtained in the integrated respiratory gasmeasuring system are a consequence of the relocation of the electronicsinto the gas measurement system. For example, this relocation hasaffected aspects of the design of interface cable 120, such as thenumber of conductors, shielding requirements, and consequently thethickness, weight and cost of the cable. The cable requires fewerconductors and so is smaller, lighter and more flexible providing lessload and drag forces on the sensor. The exemplary embodiment uses 7wires and a shield, whereas conventional devices use 16 wires and twoshields.

The present invention has a number of additional advantages overconventional gas measuring systems, including flexibility/simplifiedinterfacing to a host system 70, and increased immunity toradiofrequency interference. With a simplified hardware and softwareinterface, host system 70 only requires a simple and small connectorwired to a serial port, and a couple of supply voltages. In clinicalapplication, adding weight to the patient circuit near the ET tube isalways of concern, especially for pediatric and neonatal applications.The present invention offers a significant improvement in this regard,because the weight and potential resulting drag of the cable can bereduced. Existing cables to host systems are thicker in diameter,heavier and less flexible.

Conventional gas measurement systems, with components at or near thepatients airway, often have difficulty meeting the existing immunitystandard of 3 volts/meter. Updates to medical device electromagneticcompatibility international standards have raised this test level to ashigh as 20 volts/meter. Compliance of these standards with existingdesigns would be very difficult and expensive because of thesusceptibility to interference of analog signals transmitted through acable. In the present invention, the need to transmit analog signals inthe cable to the host system is eliminated and all the components andsignals susceptible to RFI are located near the sensing elements in thegas measurement system.

The elimination of the need for all the complex external interfaceelectronics leads to greatly reduced system cost. The efficient use ofinterconnection technologies such as rigid-flex circuit boards, andother manufacturing efficiencies result in a total system cost that islower than the cost of the existing mainstream gas measurement systemsalone.

Integration of the measurement and signal processing electronics of thegas measurement system increases the waste heat generated within gasmeasurement system 100. The compact nature of the design requirescareful consideration of the thermal design. For example, gasmeasurement system 100 is configured to permit the waste heat producedby the emitter and the electronics of the gas measurement system to heatthe windows of the airway adapter to reduce fogging. These features ofthe present invention allow the ceramic heater (also known as the caseheater) that has been used in conventional gas measurement systems to beeliminated. Additionally, the elimination of the ceramic heater, alongwith other efficiencies in the design, have permitted the total powerconsumption for the invention to be reduced from approximately 5 Watts(W) to 1.25 W.

FIG. 1 is a perspective view of gas measuring system 100 coupled to hostsystem 70 and configured to be removably secured to airway adapter 40,which is assembled with the components of a patient breathing circuit20. Airway adapter 40 is typically assembled in breathing circuit 20between an elbow 25, which is a connection to a patient interface, suchas a mask or endotracheal tube, and “Y” piece 30 which is connected to apositive pressure generator such as a ventilator. Host system 70provides the power to gas measurement system 100, receives the gasconcentration signal, and derived measurements outputted from the gasmeasurement system, and in the case where the gas concentration signalis the carbon dioxide concentration signal, displays measurements suchas: (a) the concentration of carbon dioxide in a patient's exhalations,(b) inspired carbon dioxide, (c) respiration rate, and (d) end tidalcarbon dioxide.

As noted above, cable 120 communicates gas measurement system assembly100 with host system 70. A distal end 110 of cable 120 is securely andremoveably connected to the host system. A proximal end 123 of cable 120includes a strain relief element 130 that permits tension to be appliedto cable 120 without affecting the conductor within. Power is providedto the gas measurement system from the host through the cable. However,the present invention also contemplates that the gas measurement systemmay be battery powered with either an integrated or separate batterypack and communicate its data wirelessly to the host system, therebyeliminating the need for cable 120. Wireless communications usingprotocols known in the art, such as Bluetooth, Zigbee, UWB used in bodyarea networks (BAN) and personal area networks (PAN) are contemplated.The gas measurement system may also be connected via a cable to a hub,which integrates the signals from gas measurement systems with otherphysiological measurement.

The end sections of airway adapter 40 (FIGS. 1 and 3) are designed forconnection to patient interfaces and breathing systems. For example, theairway adapter may be disposed between an endotracheal tube (not shown)inserted in a patient's trachea and the breathing circuit of a positivepressure generator or ventilator 75. Gas measurement system 100, in theexemplary embodiment, is used to measure the carbon dioxide and oxygenlevels of a patient. The particular airway adapter 40 illustrated inFIGS. 1 and 3 is not, by itself, part of the present invention. As suchthe present invention contemplates that the gas measurement system ofthe present invention can be used with any conventional airway adapter,including absorption or luminescence quenching adapters. An adapter thathas been adapted to measure gases via both infrared absorption andluminescence quenching is disclosed in U.S. patent application Ser. No.09/841,451 to Mace et al., U.S. Pub. No. 2002/0029003 (“the '451application”), the contents of which are incorporated herein byreference. Airway adapter 40 is typically molded from poly-carbonate ora comparable polymer.

An exemplary embodiment of the present invention shown in FIGS. 3 and14, airway adapter 40 has a generally parallelepipedal center section 42and two cylindrical end sections 44 and 46 with a sampling passage 47extending from end-to-end through the adapter. End sections 44 and 46are axially aligned with center section 42. Central section 42 providesa seat for gas measurement system 100. An integral, U-shaped casingelement 48 positively locates gas measurement system 100 endwise on theadapter and, also, in that transverse direction indicated by arrow 50 inFIGS. 1 and 3. Arrow 50 also shows the direction in which airway adapter40 is displaced to assemble it to gas measurement system 100. Apertures52 and 54 are formed in center section 42 of airway adapter 40.

With gas measurement system 100 assembled to the airway adapter, theseapertures are aligned along an optical path 56 in FIG. 14. Optical path56 extends from a source assembly or emitter 400 in gas measurementsystem 100 transversely across airway adapter 40 and through the gas orgases flowing through the airway adapter. The optical path continuesfrom the airway adapter to a detector assembly 300 in gas measurementsystem 100. To keep the gases flowing through airway adapter 40 fromescaping through apertures 52 and 54 without unacceptably attenuatingthe infrared radiation traversing optical path 56, and to keep foreignmaterial from the interior of the airway adapter, these apertures aretypically sealed by infrared radiation transmitting windows 58 and 60.

FIG. 4 is an exploded view of a gas measurement system 100, whichincludes a polymeric cover 210 and a gas measurement systemelectro-optical assembly 220. Gas measurement system electro-opticalassembly 220, which is perhaps best shown in FIGS. 4 and 7, includes thefollowing: (a) an infrared radiation source assembly 400 (shown ingreater detail in FIGS. 12-13), (b) an infrared radiation detectorassembly 300 (shown in greater detail in FIGS. 8-11) and (c) an optionalluminescence quenching measurement circuit board 235. In the assembledgas measurement system, strain relief 130 is held in place by walls 251and 252 provided a base 250 and cover 210. Wall 214 which mates withwall 252 when the cover is attached to the base, which is accomplishedusing any conventional technique, such as a snap-fit or friction lockconfiguration.

Gas measurement system electro-optical assembly 220 is shown in FIG. 4assembled with a flex circuit 230, a bracket 232, and a circuit board235, and an optical assembly, generally indicated at 240, which includesthe optical elements for the gas measurement system. The source anddetector assemblies are coupled to “U” shaped base 250 and mechanicallyand electrically connected to the flex circuit board, which is foldedaround these assemblies and attached to base 250. This assembly allowsthe performance of the gas measurement system's active components to betested as a unit rather than individually before assembly. As aconsequence, it is not necessary to wait until a gas measurement systemis completely assembled to determine whether it will meet performancespecifications. The result is significant cost savings, an objectivethat is furthered by the reduction of wiring and a significant reductionin the expense of assembly.

FIG. 5 is an exploded view of gas measurement system electro-opticalassembly 220 with flex circuit 230, bracket 232, and luminescencequenching measurement circuit board 235 separated from gas measurementsystem optical assembly 240. Flex circuit 230 comprises rigid boardportions 225, 226, 227, and 228 (see FIG. 15). The rigid portions arejoined to each other by flexible portions. The flex circuit boardincludes the analog and digital circuitry required to drive the infraredsource and to convert the signals from the detector assembly into anoutput values for infrared absorbing gases, such as carbon dioxide,and/or to convert the signals from the luminescence quenching assemblyinto output values for gases, such as oxygen. Circuit board 235 includesthe circuitry and optical components for the measurement of oxygen vialuminescence quenching techniques. Optical assembly 240 includesdetector assembly 300, source assembly 400, and heater flex circuit 245for controlling the temperature of the oxygen film. Heater flex circuit245 is assembled with gas measurement optical assembly 240 at top of “U”shaped base 250. Pins 246 at distal end of heater flex circuit 245 areinserted into corresponding holes 237 in end portions of luminescencequenching measurement circuit 235 prior to soldering. Similarly, pins381 of detector flex jumper 380 are inserted into corresponding holes231 along an edge of board portion 226 of flex circuit 230.

FIG. 6 is an exploded view of gas measurement system 100 showing thecover, the electronic circuit boards, and the gas measurement systemoptical assembly.

Gas measurement system electro-optical assembly 220 with flex circuit230, bracket 232, and circuit board 235 are shown separated from gasmeasurement system optical assembly 240.

FIG. 7 is an exploded view of gas measurement system optical assembly240 showing structural base member 250, detector assembly 300, andsource assembly 400. Base member 250 of gas measurement system 100supports source assembly 400 in a source assembly compartment 253 andsupports and detector assembly 300 in a detector assembly compartment254. A generally rectangular gap 66 is disposed between compartments 253and 254. Gap 66 is configured to engage the central section 42 of airwayadapter 40. Defined in large part by the side walls and rims of basemember 250, two pairs of complementary cavities in a first end section258 and a second end section 257 cooperate to define an infraredradiation source compartment 253 and an infrared radiation detectorcompartment 254, respectively. Gas measurement system base member 250may be molded from a polycarbonate or any other appropriate polymer. Inthe illustrated exemplary embodiment, base member 250 has a flat sidewall and an integral rim oriented at right angles to the side wall.

A source aperture 256 is defined in a wall of the housing to provide anoptical path for the radiation produced by the source assembly 400 toenter the sample cell portion of the airway adapter. A detector aperture255 is defined in a wall of the housing to provide an optical path forthe radiation passing exiting the airway adapter to reach detectorassembly 300. In the illustrated embodiment, a luminescence quenchingaperture 260 is also provided in the housing to measure the luminescenceof the material quenched by the oxygen in the sample gas. It is to beunderstood that the luminescence quenching feature of the presentinvention and the absorption feature of the present invention can beused alone or in combination. Thus, depending on whether one or both ofthese gas measuring techniques are used, apertures 255, 256, and 260 canbe eliminated.

FIG. 8, an exploded view of detector assembly 300 of gas measurementsystem 100, and includes a detector optical assembly 350 (FIG. 9),detectors 340 and 345 mounted on a heat sink 330, a heat sink spacer320, and a detector assembly circuit board 310. Heat sink 330 is coupledto heat sink spacer 320, which is attached to a detector assemblycircuit board 310. The resulting support assembly 325 is assembled todetector optical assembly 350 by aligning holes 335, 336, and 337 in anoptical block 370 with corresponding locator pins on heat sink 330.Detector optical assembly 350 includes optical components, such as lens364, filters 356 and 358, mirror 354, and beam splitter 352, and isassembled with detector support assembly 325. See FIG. 9.

Mounted in a recesses of heat sink 330 are data and reference detectors340 and 345, which are aligned in the same plane (i.e., co-planar),thereby permitting more effective temperature regulation of thedetectors. These detectors are preferably fabricated with lead selenidedetector elements, because of the sensitivity which that materialpossesses to infrared radiation having wavelengths, which are apt to beof interest. Additionally, lead selenide data and reference detectors340 and 345 are extremely temperature sensitive. It is, therefore,critical that these two detectors be maintained at the same temperature,preferably within the tolerance of not more that 0.02° C. Detectors 340and 345 are maintained at the selected operating temperature by adetector heating system that includes detector heating elements 391 and392, a temperature monitoring thermistor (not shown), and anoperating/control circuit (not shown), which is located in the detectorassembly circuit board 310 and flex circuit 230.

Detectors 340 and 345 are connected to detector assembly circuit board310 to which a biasing voltage is applied across the identicallyconfigured and dimensioned infrared radiation sensing elements portionsof the detectors. Gaps between the detectors and the boundaries of thedetector-receiving recesses in isothermal support serve to electricallyisolate the detectors from the conductive, isothermal support. Athermistor (not shown) is positioned so as to be centrally located in agroove 322 of heat sink spacer 320. Heating elements 391 and 392 arelocated at the ends of heat sink 330 and are in intimate contact withthe heat sink. Heating element 391 and 392 include a flex circuitportion having a distally located surface mount resistor for delivery ofheat.

Two pins 388 and 389 are provided in the heating elements to connectthem to detector assembly circuit board 310. The flex circuit portion ofheating elements 391 and 392 are placed in intimate contact with heatsink 330. In the exemplary embodiment, an epoxy, preferably with a highthermal conductivity, is employed to adhere the flex circuit portion ofeach of the heating elements to heat sink 330. Pins 388 and 389 ofheating elements 391 and 392 insert into corresponding holes 386 and 387on detector assembly circuit board 310. A detector flex jumper 380interfaces detector assembly circuit board 310 to board portion 226 offlex circuit 230. Pins 382 of detector flex jumper 380 insert intocorresponding holes 383 along an edge of detector assembly circuit board310. Pins 381 of detector flex jumper 380 inserted into holes 231 ofboard portion of flex circuit 230.

Detector optical assembly 350 will be described with reference to FIGS.9-11. Detector optical assembly 350 includes beam splitter 352, mirror354, filters 356 and 358, and detector lens 364. The beam splitter has agenerally parallelepipedal configuration. This component is fabricatedfrom a material such as silicon or sapphire, which is essentiallytransparent to electromagnetic energy in wavelengths of interest. Theexposed front surface of the beam splitter is completely covered with acoating capable of reflecting that electromagnetic energy impinging onthe beam splitter which has a wavelength longer than a selected value.In the illustrated exemplary embodiment of the invention, the coatingwill reflect to data filter 356 and data detector 340 energy having awavelength longer than about 4 microns. The energy of shorterwavelengths is, instead, transmitted through beam splitter 352 to mirror354 and to reference filter 358 and reference detector 272.

Beam splitter 352 is fixed in place by epoxying or otherwise bonding thebeam splitter to ledge 351 which is integral to optical block 370. Thisaccurately positions beam splitter 352 within optical block 370 with theadvantage that subsequent adjustment of the beam splitter orientation isnot required. Similarly, mirror 354 is fixed in placed by epoxying orotherwise bonding the mirror to ledge 353, which is also integral tooptical block 370. Also, the electro-optical assembly of the presentinvention has an optimized focal length which makes it possible toemploy a smaller, less expensive detector assembly of the gasmeasurement system.

Bandpass filters 356 and 358 limit the infrared radiation energyrespectively reflected from and transmitted by beam splitter 352 andimpinging upon data and reference detectors 340 and 345 to energy inselected bandwidths. In the exemplary embodiment and use of theinvention under discussion and depicted in the drawing, referencedetector filter 358 is nominally centered on a wavelength of 3.7microns. Such a filter transmits maximum energy near the carbon dioxideband absorbed by data detector 340. This absorption of maximum energy inan adjacent bandwidth is selected so that the output from referencedetector 345 will be at least as large as the output from data detector340. This contributes markedly to the accuracy of the gas concentrationindicative signal subsequently obtained by ratioing the data andreference signals.

Data detector bandpass filter 356 is nominally centered on a wavelengthof 4.26 microns. The carbon dioxide absorption curve is fairly narrowand strong, and bandpass filter 356 centers the transmission band withinthat absorption curve. Therefore, if there is a change in carbon dioxidelevel in the gas(es) being analyzed, the maximum modulation for a givenchange in carbon dioxide level is obtained. Data and reference bandpassfilters 356 and 358 are bonded in recesses 360 and 362 of optical block370. When optical block 370 is attached to the detector circuit board,data and reference bandpass filters 356 and 358 are aligned with dataand reference detectors 340 and 345, respectively.

All of the energy over the entire and same span of infrared radiationbeam propagated along optical path 56 and reaching detector assembly 300with a wavelength longer than the selected cutoff is reflected to datadetector 340. Similarly, energy with a shorter wavelength is transmittedthrough beam splitter 286 to reference detector 345. Because of this,the physical relationship of detectors 340 and 345 discussed above, andthe dimensioning and configuration of the energy intercepting sensingelements of those detectors, both detectors “see” the same image of thebeam of electromagnetic energy. This contributes markedly to theaccuracy afforded by detector assembly 300.

In other words, and optically, with the data and reference detectors 340and 345 accurately positioned relative to each other, and beam splitter352 situated in the manner described above, these components function asif the two detectors were precisely stacked one on top of the other.Therefore, electromagnetic energy from the beam reaches both detectorsin spatially identical fashion. By making the two detectors 340 and 345spatially coincident from an optical viewpoint and electronicallysampling the detector outputs at the same times, the adverse effects onaccuracy attributable to foreign material collecting on either of theabove-described airway adapter optical windows 58 and 60, the window 460of source assembly, or a subsequently described window 364 of detectorassembly 300 are also effectively eliminated by the subsequent ratioingof the data and reference detector output signals.

The electromagnetic energy in the beam propagated along optical path 56reaches beam splitter 352 through an aperture 366 defined in a frontwall 339 of optical block 370. An infrared radiation transparent lens364, typically made of sapphire, spans aperture 366 and keeps carbondioxide and other foreign material from penetrating to the interior ofoptical block 370. Lens 364 is bonded to the optical block in anyconvenient and appropriate manner.

Infrared radiation source assembly 400 will now be described withreference to FIGS. 12 and 13. Infrared radiation source assembly 400emits infrared radiation in the form of a beam 480 (see FIG. 16), whichpropagates along optical path 56. The infrared radiation source assemblyincludes an infrared radiation emitter 445, commutators/lead frames 446and 447 disposed in a source ring assembly 420, and a lens 460 mountedin a lens holder 440 attached to source ring assembly 420. Infraredradiation emitter 445 includes a substrate formed from a material havinglow thermal conductivity. This is significant because it dramaticallyreduces the power required to heat the emitter to the operatingtemperature. When current is applied across a emissive layer 448 ofemitter 445, heating up the emissive layer and substrate, the substrategrows or increases in length due to thermal expansion, but this growthis accommodated by an elastic bonding agent rather than beingconstrained. As a consequence, the stresses, which would be imposed uponemitter if both ends were rigidly fixed, are avoided, eliminating thedamage to emitter or complete failure of that component which mightresult if high mechanical stresses were imposed upon it.

Emitter 445 of source assembly 400 is energized to heat it to anoperating temperature in which it emits infrared radiation in anappropriate range of bandwidths by effecting a flow of electricalcurrent through emissive layer 448 from an appropriate power supply. Thepower supply is connected to emissive layer 448 via electrical leads 451and 452. These leads are soldered or otherwise physically andelectrically connected to at opposite ends of commutators 446 and 447.

Commutators 446 and 447 are installed in source ring 420 of sourceassembly 400. The environment in which this component operates can reachan elevated temperature due to heating by emissive layer 448 of infraredradiation emitter 445. The source ring is, therefore, fabricated of apolymer that remains structurally stable at the temperatures it reachesduring the operation of infrared radiation emitter 445. In theillustrated exemplary embodiment, source ring 420 has a cylindricalconfiguration with an integral wall 454 and base 453. Projecting in thesame direction from base 453 are assembly locating bosses or lugs 456,457, 458, and 459. Spaced apart lugs 456 and 457 and the complementary,spaced apart lugs 458 and 459 embrace the opposite sides of commutators446 and 447. Bosses or lugs 461 and 462 separate the commutatorsegments, providing gaps therebetween to electrically isolate the twocommutator segments. This is necessary so that a voltage differentialcan be created across emitter 445 to cause operating current to flowthrough the emitter.

Referring now to FIGS. 14-16, as well as FIGS. 12 and 13, infraredradiation outputted by emissive layer 448 of infrared radiation emitter445 is focused and propagated along optical path 56 through a lens 430disposed in a lens holder 440. Foreign material is kept from theinterior of the infrared radiation source assembly 400 by a sapphire orother infrared radiation transmitting window 460 spanning and closingaperture in which lens 441 is mounted. Window 460 is cemented orotherwise bonded to a ledge or groove 442 formed in lens holder 440 ofinfrared radiation source assembly 400.

Energy in a specific band is absorbed by the gas of interest flowingthrough the airway adapter (typically carbon dioxide) to an extentproportional to the concentration of that gas. Thereafter, theattenuated beam of infrared radiation passes through the aperture 306 inthe front wall 308 of the detector portion of housing 210, isintercepted by beam splitter 352, and is either reflected toward datadetector 356 or transmitted to reference detector 358 after reflected bymirror 354. Bandpass filters 356 and 358 in front of those detectorslimit the energy reaching them to specified (and different) bands. Eachof the detectors 356 and 358 outputs an electrical signal proportionalin magnitude to the intensity of the energy striking that detector.These signals are amplified by electronic circuitry on detector systemcircuit board 310 and conducted to a digital signal processor on boardportion 225 of flex circuit 230. The processor typically ratios thesignals from the detectors to generate a third signal accuratelyreflecting the concentration of the gas being monitored.

Optical path 56, the distance transversed by the infrared radiationbetween windows 58 and 60 mounted in apertures 52 and 54, respectivelyand located within integral “U” shaped casing element 48 of airwayadapter 40, is shown. The optical alignment features of base 250 arereadily apparent from the cross-sectional view. Features of lens holder440 attached to source ring assembly 420 serves to properly align sourceassembly 400 within base 250. Similarly, features of detector opticalassembly 350 serves to properly align detector assembly 300 within base250.

Luminescence quenching optical system 236 is assembled to luminescencequenching measurement circuit board 235. Luminescence quenching opticalsystem 236 includes excitation source 237 and detectors (not shown). Anexemplary excitation source consists of a green light emitting diode.Heater flex circuit 245 is electrically interfaced to luminescencequenching measurement circuit board 235 as noted above. As noted above,an exemplary embodiment of a luminescence quenching optical system 236suitable for use in the present invention is disclosed in the '451application.

FIG. 15 is a flattened view of the assembled components of the gasmeasurement system prior to placement in the housing. Prior toassembling detector assembly 300 and source assembly 400 to “U” shapedbase 250, these assemblies are physically and electrically interfaced toflex circuit 230. Detector assembly 300 is connected to board portion226 of flex circuit 230 with detector flex jumper 380. The ends of leads443 and 444 (FIG. 12) of source assembly 400, and the connectors incable 120 are connected to board portion 227 of flex circuit 230. Toassemble flattened electrooptical assembly 222 to base 250, sourceassembly 400 and detector assembly are attached to base 250. Boardportion 225 of flex circuit 230 is placed at top of the “U” of base 250.Board portion 228 is folded to fit in detector assembly compartment 254and board portion 227 is folded to fit in source assembly compartment253.

FIG. 16 is a ray tracing of the optical path within the assembled gasmeasurement system. Rays 480 in FIG. 16 are illustrative only and shownas if emissive layer of emitter 445 is a point source. The infrared raysfrom emitter 445 are collimated by half-ball lens 430. The concave shapeof airway side of the lens serves to “focus” the rays into a parallel.The rays impinge upon infrared absorptive gases and substances that arewithin the airway adapter and are absorbed and scattered. The remainingrays pass through the window of airway adapter and entered detectorassembly 300. The rays pass through lens 364 and are collimated/focusedonto beamsplitter 352, where approximately half of the rays arereflected and pass through filter 356 and detector 356, and the otherhalf are transmitted and reflected by mirror 354 onto filter 358 anddetector 358.

FIG. 17 is a block diagram of the gas measurement system according tothe principles of the present invention. A microprocessor 510 providesthe control, measurement, and signal processing functions of thisinvention. An exemplary processor is the TMS320F2812 DSP manufactured byTexas Instruments. Microprocessor 510 provides the source timing signalsto source assembly 400, which is driven by a pulsed voltage of 5.0 V DCin a uni-polar fashion. A source emitter watchdog 511 monitors thesource pulse width and maintains it within an allowable window. A systemreset generator 520 is employed during the power up sequence, so thatthe processor will only reset once a stable voltage is reached andduring the down sequences so that an orderly power down sequence willoccur.

The executable program stored in an EEPROM 530 is communicated tomicroprocessor 510. Data and reference channel signals from detectorassembly 300 are amplified by a digital attenuation 540 prior to analogto digital conversion within microprocessor 510. A detector heater 590located within detector assembly 300 is controlled by a feedback loop bymicroprocessor 510. The low level signals from the detectors are ACcoupled, amplified, and level shifted to allow for complete signalacquisition. Dual sample and hold stages within the ADC providesimultaneous sampling of the data and reference channels. Active gainand offset adjustment compensate for the optical and electronicvariables in the signal chain. Detector heater driver controls thedelivery of energy to detectors while detector thermistor driverprovides the thermistor signal to the processor. A control algorithmsuch as a PID controller serves to regulate the temperature of 50° C. towithin ±0.02° C. The detector heater is powered by the +5 V DC supply,which is also used to power the analog circuitry regulator. Serialdriver 570 communicates bi-directionally using a transmit and receiveline denoted Tx and Rx respectively. Power supply 560 receives powerfrom VSRS and VA lines with signal return and a digital and analogground provided.

The above-described exemplary embodiment of the present invention hasshown an optical assembly with a infrared detector system in a linearconfiguration that includes a single beamsplitter, single mirror, twofilters, and two detectors. This configuration is well suite to measurea single gas flowing through the sample cell. However, there is anincreasing need to measure additional gasses using a transducer that isthe same size as that used to makes a single gas measurement. To thisend, the present invention contemplates other embodiments for the gasmeasurement systems that includes an infrared spectrometer portioncapable of measuring multiple gases. For example, a four channel systemwould permit quantification of the concentrations of carbon dioxide,nitrous oxide, and certain anesthetic agents, along with a referencechannel. The present invention may also be adapted as an efficientnon-dispersive infrared multi-channel gas analysis configuration thatuse one or more of the following novel features and combinations:

-   -   a) multiple dichroic beam splitters that divide the spectrum in        a binary sequence, with narrow bandpass filters to select        specific wavelengths;    -   b) combinations two or more dichroic splitters on a single        substrate;    -   c) geometrical configurations in which all detectors are        disposed on a single plane, and can use a single turning mirror        for multiple channels;    -   d) a broadband bandpass filter in place of two dichroic        splitters;    -   e) toroidal focusing mirrors, and in combination with sapphire        or germanium lenses; and/or    -   f) lenses on both sides of a beam splitting element to compactly        provide independent control of reflected and transmitted light.

FIG. 18 is a schematic diagram of an exemplary embodiment of an opticalsystem disposed in a linear configuration according to the principles ofthe present invention. The optical system in the this embodimentconsisting of four channels, each having a narrow bandpass filter anddetector. Each of the filter/detector assemblies 611, 612, 613, and 614use similar detectors, but filters each with different passbands. Thebeam from the infrared source, after having passed through the samplecell, enters the optical system. This beam is indicated by referencenumeral 600 in the figures. Beam 600 strikes a first dichroic beamsplitter 601. First dichroic beam splitter 601 may be configured to passeither the shortest wavelength of interest or pass the longestwavelength of interest. All other wavelengths would be reflected. Theother wavelengths, or channels, are split off from the reflected beam insequence by second and third dichroic beam splitters 602 and 603. Thesequence of the beam splitter wavelengths is somewhat arbitrary. Thefinal element, plain mirror 604, reflects the final channel, to thedetector or filter/detector assembly 614. The use of this mirror permitsall detectors to be on the same plane (i.e., coplanar).

FIG. 19 illustrates the filter characteristics of short (low) pass beamsplitters 605, 606, and 607 as a function of wavelength relative to thefilter characteristics of bandpass filters 615, 616, 617, and 618 foreach of the channels in the linear system of FIG. 19. Each detector hasa narrow band filter to select the required wavelength for detectionwith more specificity than may be done with dichroic beamsplitters. Notethat the logic could be inverted, in the sense that the firstbeamsplitter could pass the longest wavelength, 618, and reflect theother wavelength to filters 615, 616, 617. Then the followingbeamsplitters could be short pass, in which case the sequence would be617, 616, and 615, or they could be long pass, with a sequence 615, 616,and 617.

Alternatively, long and short pass could be mixed in certain sequences.Note that dichroic beam splitters are used instead of the moreconventional broadband beam splitters in order to materially improve theamount of signal energy that will reach the detectors, especially thelast detector. This linear system has the advantages of a simple designand all detectors are on the same plane. However, the beam spreadssubstantially along the path length to the final detector, so the energycollected by the last detector is less than previous detectors.

FIG. 20 is schematic diagram of an optical system having a zigzagconfiguration. This system makes use of the fact that a dielectricbandpass filter will reflect all wavelengths that are not transmitted.In effect, there is a conservation of energy. In the case of the zigzag,the first element is a mirror 621. Each of the beamsplitters 626, 627,628, and 629 are narrow bandpass filters. Because all energy that is notselected for a particular channel is reflected on to other channels, thesequence of filter/detector assemblies 622, 623, 624, and 625 arearbitrary. Note that each filter must be designed to operate at thechosen angle (typically 40° to 45°). The system has a shorter pathlength, and a lower parts count, because the narrow bandpass filtersperform a dual function of sequencing the channels, as well as narrowlydefining the desired wavelength. The detectors are now on two planes,but the detector assemblies are identical. The system as drawn shows thelight path from the source to final detector in the same plane. For easein packaging, the assembly following the mirror 621, may be rotated 90degrees about the optical axis, so that the source optical axis would benormal to the plane of the zigzag.

FIG. 21 is schematic diagram of an optical system having a square arrayconfiguration. Dichroic beam splitters are used in a more direct binaryselection process. For example, using the characteristics of the filtersand beamsplitters shown in FIG. 21, the first beamsplitter 631 may beset at 4 microns to divide the spectrum of interest in half. Thereflected half is split again at 4.4 microns, with the reflected partgoing directly to the narrow bandpass filter/detector assembly 632,while the pass part is subsequently reflected at mirror 636 to narrowbandpass filter/detector assembly 633. The half that is passed bybeamsplitter 631 is reflected at mirror 638, to beamsplitter 637, whichis set at 3.45 microns. As in the first described leg, beamsplitter 637splits and directs the beam to narrow bandpass filter/detectorassemblies 634 and 635. The paths of the beam channels 1 and 2, andchannels 3 and 4 have been rotated about the optical axis at mirror 636and beamsplitter 631 respectively. By this device of “twisting thelegs”, all the detectors can be placed in close proximity on the sameplane. Additionally, in this system, the two mirrors, shown as mirror636, can be manufactured as a single piece, and the beamsplitters, shownas beamsplitter 634, can also be formed on a single substrate.

It should be noted that the combination beamsplitter can be built as apair of overlapping dichroic beamsplitters, with one on each side of asapphire substrate, or it could be built as a wide bandpass filter,where the band edges form the wavelength splitting function. Thefollowing described systems may appear somewhat similar in generalarchitecture, but they contain focusing elements in the forms ofsapphire lenses, concave spherical mirrors, or concave asphericalmirrors.

The system advantage to added focusing elements is a greatly improvedenergy collection efficiency at each detector. Without the focusingelements, the beam from the source will be much larger than thedetectors at the detector plane. This oversize comes about for 2reasons: system magnification, and aberrations. The ratio of thedistance from the source mirror to the focal point to the distance fromthe source to the source mirror is the magnification. Depending on wherethe focus is set, the magnification will be in the range of 8 to 10. Thesource is about 0.02″ in diameter, so an image at the detector planewill be in the range of 0.16″ to 0.2″. But the detectors are typically0.08″ diameter (larger detectors are possible, but the cost risesquickly with size.). Further, although the source mirror gives a verygood image at the center of the field, points at the edge of the sourceare aberrated, which adds to the basic image magnification. However, ifpositive focusing elements can be placed in proximity to the detectors,the magnification can be radically reduced, and the aberrations alsoreduced in absolute terms. In the instant systems, a compressed beam canimprove the detection efficiency by a factor of four or more. Note thatin view of the aberrated condition of the beam, it is not feasible for asimple lens to form a good image on the detector, but in fact since theobjective is just to collect as many infrared radiation rays aspossible, a good image is not required.

FIG. 22 is schematic diagram of an optical system having a linear systemconfiguration with lenses included in the optical assembly. Thisconfiguration is similar in layout to the linear configuration of FIG.18, with the addition of a lens 645 inserted along the optical path,typically between beamsplitter 642 and 643 and filter/detectorassemblies 652 and 653. The function of the lens is to compress the beamenergy to detector assembly 653 and detector assembly 654, which willimprove the efficiency of detection in those channels. The action of thelens is to reduce the magnification of the system. In addition, lenses655-658 can be added to each channel, thereby reducing the magnificationfurther, and improving and equalizing the efficiency of all detectors.

FIG. 23 is schematic diagram of an optical system having a zigzagconfiguration with lenses again included in the optical assembly. Inthis configuration, which is essentially a modification of that shown inFIG. 20, lenses are added at each channel to compress the beam size. Ifa single lens was added between the beam splitter and the detector, onlythe transmitted beam would be affected, and the reflected beam wouldexpand more than desired by the last channel. But if a single lens isadded in front of the beamsplitter that is strong enough to compress thebeam suitably for that detector, the effect on the reflected beam wouldbe doubled, and would be too strong.

The present invention solves this dilemma by splitting the lens into twocomponents, one part on either side of a narrow bandpass filter. Forexample, split lens/filter assembly 669 comprises lens 666 and 668 andfilter 667. By splitting the lens in this way at each channel, the partthat is transmitted and the part that is reflected each gain the effectof a full lens. Alternatively, the two lenses at each channel can bedifferent, so that for example the transmitted beam can be more stronglycompressed as compared to the reflected beam. Note that with thissystem, the dichroic beam splitters are eliminated.

FIG. 24 is schematic diagram of an optical system having a doglegconfiguration. This configuration is similar to the square array in thatthe dichroic beam splitters are used to split the beam by wavelengths ina binary manner. Dichroic beamsplitter 682 does the first division. Thereflected beam goes to reflector 681. This is one of four focusingmirrors that are added to compress the beam to improve detectionefficiency. These mirrors can be spherical, but, preferentially, theyare aspherical. This preference arises because a spherical element at ahigh angle of incidence will produce two different focal points, one inthe plane of incidence, the other perpendicular to that. In other words,such a mirror will produce an astigmatic image. By making the radius ofcurvature different in the two axes, the astigmatism can be corrected.Aspheric is a general term for a surface that is not spherical. Themirrors shown here are toroidal, a sub-set of the general class. In thepresent case, even though a good image is not required, an asphericmirror can produce a more uniform circular beam pattern.

The reflected and re-focused beam is split again at dichroicbeamsplitter 675. Again the reflected beam is re-focused on to thebandpass filter/detector assembly 672. The transmitted beam goes tofilter/detector assembly 671. The transmitted beam from beamsplitter 682is re-focused by focusing mirror 683, and split by beamsplitter 678. Aswith the other two channels, the beam goes to filter/detector assembly674, or to filter/detector assembly 673 via focus mirror 677. Note thatthis system provides high collection efficiency, and a compactsingle-plane detector array.

FIG. 25 is schematic diagram of an optical system having a snakeconfiguration. The “snake” architecture is similar to the linear array,except that focusing mirrors 691-694 are added to each channel. Theinitial split is done by dichroic beamsplitter 681, followed bybeamsplitters 682 and 683, and mirror 684. The focusing mirrors can bespherical, but aspherical mirrors make a significant improvement incollection efficiency. In an exemplary embodiment of the presentinvention, the mirrors are made in a single long molding. Thefilter/detector assemblies 685, 686, 687, and 688 consist of a narrowbandpass filter and detector, the same as in the other previouslydescribed embodiments.

FIG. 26 is schematic diagram of an optical system having a tunnelconfiguration. Infrared energy can be distributed to a planar array ofdetectors in a different way. Energy from the source 698 can be directedinto a pipe 696 by mirror 699, or what may be termed an optical tunnel.If the interior of the pipe is a mirror, and if the pipe is long enough(of the order ten times the diameter), the energy at the end of the pipewill be well mixed, geometrically. That is, any structure in the inputbeam, for example, due to an imperfection in the airway, or a drop ofliquid on an airway window, will not be detectable at the output(although the overall energy level may be down). Similarly, if the inputbeam is not exactly in the right place, or at the right angle, therewill be essentially no effect at the output.

The idea of this embodiment to put a planar array 697 of narrow bandpassfilters and associated detectors at the output. The action of the tunnelwill distribute the energy symmetrically to the detectors. Note that theenergy at the output is radially symmetric, but not uniform over thearea. The system as described is not efficient, because the pipe outputis circular, while the array is square (for four detectors), andfurther, the area of each detector is a fraction of the total outputarea. This loss in efficiency can be alleviated by making the pipesquare to match the detector array, or alternatively, a set of funnelscan be placed at the output. These funnels would, as a group, accept allof the energy from the pipe, divide it multiple ways to match the numberof channels, and concentrate the energy down to the detector size. Inthe figure, the side of the pipe (and the source mirror) has been cutaway for illustration. The detector plane does not show the array.

FIG. 27 is a side view of an embodiment of a four channel optical system700 disposed in a linear configuration. Infrared radiation entersdetector/optical assembly 700 by first passing through lens 710. Theinfrared radiation is then successively split and reflected bybeamsplitters 743, 753, and 763. The transmitted infrared radiationpasses through filters 740, 750, and 760 prior to detectors 745, 755,and 765, respectively. The remaining infrared radiation that passesthrough beamsplitter 763 is reflected by focusing mirror 720 throughfilter 770 and onto detector 775. Heaters 735 and 730 serve to maintainthe detector block 780 at a constant temperature.

In the above-described embodiments, multiple absorption type detectorassemblies are provided to detect more than one gas constituent in thegas flowing in the sample cell. It is to be understood that the presentinvention also contemplates providing multiple gases for luminescencequenching type of gas detectors, either alone or in combination with theabsorption type of detectors. Multiple luminescence quenching type ofgas detectors would need multiple sources, detectors, with filters andmultiple chemistries on the substrate of the airway adapter.

The present invention also contemplates providing display 800 (see FIG.3) on the housing of the gas measurement system. The display can be anysuitable display, such as an LED, OLEDs, LCD, etc. Providing a displayon the housing of the gas measurement system permits the clinician orother user to visualize warnings or advisory messages, waveforms,trends, and other relevant information directly from the unit proximateto the patient, without having to reposition themselves to see aconventional monitoring screen, which is typically necessary because ina conventional system the monitoring screen is often several feet awayfrom the patient. This would be of particular importance during anadverse clinical event that would require the immediate attention andresponse of the clinician.

Although the invention has been described in detail for the purpose ofillustration based on what is currently considered to be the mostpractical and preferred embodiments, it is to be understood that suchdetail is solely for that purpose and that the invention is not limitedto the disclosed embodiments, but, on the contrary, is intended to covermodifications and equivalent arrangements that are within the spirit andscope of the appended claims. For example, it is to be understood thatthe present invention contemplates that, to the extent possible, one ormore features of any embodiment can be combined with one or morefeatures of any other embodiment.

1. A gas measurement system comprising: a radiation source assembly; alens adapted to receive infrared radiation from the radiation sourceassembly and to collimate the received infrared radiation; a dichroicsplitter adapted to receive collimated infrared radiation from the lensand to separate the received infrared radiation into a first beam and asecond beam; a mirror adapted to receive the first beam from thedichroic splitter; a first filter adapted to receive the first beam fromthe mirror; a second filter adapted to receive the second beam from thedichroic splitter; a first detector adapted to receive the first beamfrom the first filter, wherein the first detector is a generally planarelement disposed in a first plane, and wherein the first detector isoriented such that the first beam is directed at a radiation receivingsurface of the first detector at a generally right angle; and a seconddetector adapted to receive the second beam from the second filter,wherein the second filter is a generally planar element, wherein thesecond detector is oriented such that the second beam is directed at aradiation receiving surface of the second detector at a generally rightangle, and wherein the first detector and the second detector aredisposed such that the radiation receiving surfaces of the firstdetector and the second detector are substantially parallel to oneanother.
 2. The gas measurement system of claim 1, further comprising aheat sink, and wherein the first detector and the second detector aremounted on the heat sink.
 3. The gas measurement system of claim 1,further comprising a housing adapted to be mounted on an airway adapter,wherein the dichroic splitter, the mirror, the first filter, the secondfilter, the first detector, and the second detector are disposed in thehousing.
 4. The gas measurement system of claim 3, further comprising adisplay disposed on the housing.
 5. The gas measurement system of claim3, wherein the housing has a generally U-shaped configuration having afirst leg and a second leg, wherein the dichroic splitter, the mirror,the first filter, the second filter, the first detector, and the seconddetector are disposed in the second leg of the housing, and wherein theradiation source assembly is disposed in the first leg of the housing.6. The gas measurement system of claim 1, further comprising a processordisposed in the housing and operatively coupled to the first detectorand the second detector, wherein the processor is programmed to measurea constituent of at least one gas based on an output of the firstdetector and the second detector.
 7. The system of claim 1, wherein theradiation receiving surfaces of the first detector and the seconddetector are disposed in a common plane.